How do I suspend java threads on demand?

I am working on a multithreaded game in java. I have several worker threads that fetch modules from a central thread manager, which then executes it on its own. Now I would like to be able to pause such a thread if it temporarily has nothing to execute. I have tried calling the wait() method on it from the thread manager, but that only resulted in it ignoring the notify() call that followed it.

I googled a bit on it too, only finding that most sites refer to functions like suspend(), pause(), etc, which are now marked a deprecated on the java documentation pages.

So in general, what is the way to pause or continu开发者_如何学Goe a thread on demand?

You can use an if block in the thread with a sentinal variable that is set to false if you want to halt the thread's action. This works best if the thread is performing loops.

Maybe I'm missing the point, but if they have nothing to do, why not just let them die? Then spawn a new thread when you have work for one to do again.

It sounds to me like you're trying to have the conversation both ways. In my (humble) opinion, you should either have the worker threads responsible for asking the central thread manager for work (or 'modules'), or you should have the central thread manager responsible for doling out work and kicking off the worker threads.

What it sounds like is that most of the time the worker threads are responsible for asking for work. Then, sometimes, the responsibility flips round to the thread manager to tell the workers not to ask for a while. I think the system will stay simpler if this responsibility stays on only one side.

So, given this, and with my limited knowledge of what you're developing, I would suggest either:

Have the thread manager kick of worker threads when there's stuff to do and keep track of their progress, letting them die when they're done and only creating new ones when there's new stuff to do. Or

Have a set number of always existing worker threads that poll the thread manager for work and (if there isn't any) sleep for a period of time using Thread.sleep() before trying again. This seems pretty wasteful to me so I would lean towards option 1 unless you've a good reason not to?

In the grand tradition of not answering your question, and suggest that You Are Doing It Wrong, I Offer this :-)

Maybe you should refactor your code to use a ExecutorService, its a rather good design. http://download.oracle.com/javase/6/docs/api/java/util/concurrent/ExecutorService.html

There are many ways to do this, but in the commonest (IMO), the worker thread calls wait() on the work queue, while the work generator should call notify(). This causes the worker thread to stop, without the thread manager doing anything. See e.g. this article on thread pools and work queues.

use a blocking queue to fetch those modules using take()

or poll(time,unit) for a timed out wait so you can cleanly shutdown

these will block the current thread until a module is available